The Collaborative International Dictionary of English v.0.48:

Substantial \Sub*stan"tial\, a. [F. substantiel, L.
   substantialis.]
   1. Belonging to substance; actually existing; real; as,
      substantial life. --Milton.
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            If this atheist would have his chance to be real and
            substantial agent, he is more stupid than the
            vulgar.                               --Bentley.
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   2. Not seeming or imaginary; not illusive; real; solid; true;
      veritable.
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            If happinessbe a substantial good.    --Denham.
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            The substantial ornaments of virtue.  --L'Estrange.
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   3. Corporeal; material; firm. "Most ponderous and substantial
      things." --Shak.
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            The rainbow [appears to be] a large substantial
            arch.                                 --I. Watts.
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   4. Having good substance; strong; stout; solid; firm; as,
      substantial cloth; a substantial fence or wall.
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   5. Possessed of goods or an estate; moderately wealthy;
      responsible; as, a substantial freeholder. "Substantial
      yeomen and burghers." --Sir W. Scott.
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WordNet (r) 3.0 (2006):

substantial
    adj 1: fairly large; "won by a substantial margin" [syn:
           significant, substantial]
    2: having a firm basis in reality and being therefore important,
       meaningful, or considerable; "substantial equivalents" [syn:
       substantial, substantive]
    3: having substance or capable of being treated as fact; not
       imaginary; "the substantial world"; "a mere dream, neither
       substantial nor practical"; "most ponderous and substantial
       things"- Shakespeare [syn: substantial, real, material]
       [ant: insubstantial, unreal, unsubstantial]
    4: providing abundant nourishment; "a hearty meal"; "good solid
       food"; "ate a substantial breakfast"; "four square meals a
       day" [syn: hearty, satisfying, solid, square,
       substantial]
    5: of good quality and condition; solidly built; "a solid
       foundation"; "several substantial timber buildings" [syn:
       solid, strong, substantial]

Moby Thesaurus II by Grady Ward, 1.0:

307 Moby Thesaurus words for "substantial":
   ab ovo, able to pay, absolute, abundant, actual, adequate,
   affluent, allegorical, ample, appreciable, ascendant,
   associational, authentic, authoritarian, authoritative, authorized,
   autocratic, balanced, barely sufficient, basal, basic, big,
   big-league, big-name, big-time, bigwig, bigwigged, binding, bodily,
   bumper, calculable, charismatic, charming, close, close-knit,
   close-textured, close-woven, clothed with authority, cogent,
   comfortable, commanding, commensurate, compact, compacted,
   competent, compressed, concentrated, concrete, condensed,
   congested, connotational, connotative, consequential, considerable,
   consistent, consolidated, constituent, constitutive, controlling,
   cool, corporal, corporeal, corresponding, crammed, crammed full,
   crowded, de facto, decent, definable, denotational, denotative,
   dense, dependable, dominant, double-barreled, due,
   duly constituted, durable, earthly, earthshaking, easy, effective,
   effectual, efficacious, elemental, elementary, eminent, empowered,
   enchanting, enough, equal to, essential, estimable, ex officio,
   expressive, extended, extensional, factual, faithful, faithworthy,
   fast, fiducial, figurative, firm, firm as Gibraltar, fit, fleshly,
   for real, full of meaning, full of point, full of substance,
   fundamental, generous, genuine, gluey, good, good enough, good for,
   goodly, governing, grand, great, gross, gut, hard, healthy, heavy,
   heavyweight, hegemonic, hegemonistic, high-powered, historical,
   honest-to-God, huge, hylic, impenetrable, imperative, impermeable,
   imperturbable, important, impressive, in equilibrium, indicative,
   influential, intelligible, intensional, interpretable, invincible,
   jam-packed, jammed, just, key, landed, large, large-scale, lawful,
   leading, legal, legitimate, logical, magnetic, major, man-sized,
   massive, material, materiate, meaning, meaningful, meaty,
   metaphorical, mighty, minimal, minimum, momentous, monocratic,
   name, nonporous, nonspiritual, numberless, numerous, objective,
   of the essence, official, original, packed, palpable, personable,
   persuasive, phenomenal, physical, pithy, plenty,
   plenty good enough, pointed, ponderable, positive, potent,
   powerful, predictable, preeminent, pregnant, prestigious, primal,
   primary, primitive, principal, profitable, prominent, propertied,
   proportionate, prosperous, puissant, radical, ranking, readable,
   real, referential, reliable, reputable, respectable, rich, ruling,
   satisfactory, secular, secure, self-consistent, self-important,
   senior, sensible, sententious, serious, serried, significant,
   significative, sizable, sizeable, snug, solid, solvent, somatic,
   sound, stable, staunch, steadfast, steady, stout, strong, sturdy,
   suasive, substantive, successful, sufficient, sufficient for,
   sufficing, suggestive, suitable, superior, supreme, sure, surefire,
   symbolic, tall, tangible, telling, temporal, thick, thick-growing,
   thickset, tidy, totalitarian, transferred, true, trustworthy,
   trusty, undeniable, underlying, unfailing, unflappable,
   unflinching, unindebted, unshakable, unspiritual, unwavering,
   up to, valid, vast, veritable, viscid, viscose, viscous, wealthy,
   weighty, well, well-balanced, well-built, well-established,
   well-fixed, well-founded, well-grounded, well-heeled, well-off,
   well-to-do, winning, without nerves, world-shaking, worldly,
   worthwhile